MMP9 modulates tight junction integrity and cell viability in human airway epithelia

Abstract

The family of zinc-and calcium-dependent matrix metalloproteases (MMPs) play an important role in remodeling of the airways in disease. Transcriptional regulation by proinflammatory cytokines increases lymphocyte-derived MMP9 levels in the airway lumen of asthmatics. Moreover, the levels of the MMP9 inhibitor, tissue inhibitor of metalloprotease (TIMP1), are decreased leading to increased protease activity. The mechanism by which MMP9 activity leads to asthma pathogenesis and remodeling remains unclear. Using a model of well-differentiated human airway epithelia, we found that apical MMP9 significantly increases transepithelial conductance. Moreover, apical MMP9 treatment decreased immunostaining of tight junction proteins suggesting disruption of barrier function. Consistent with this, viruses gained access to the epithelial basolateral surface after MMP9 treatment, which increased infection efficiency. All of these effects were blocked by TIMP1. In addition, loss of epithelial integrity correlated with increased epithelial cell death. Thus we hypothesized that MMP9 exerts its effects on the epithelium by cleaving one or more components of cell-cell junctions and triggering anoikis. Taken together, these data suggest that a component of airway remodeling associated with asthma may be directly regulated by MMP9.protease; adhesion; cell death THE AIRWAY EPITHELIUM SITS at the interface between the external environment and the body proper. With each inhaled breath, viruses, bacteria, pollutants, and allergens are introduced into the system, each with the potential to adversely affect the host. In the airways, mechanisms to reduce these hazards have evolved including mucociliary clearance, mucus secretion, as well as sneeze and cough. In addition, the polarized nature of the epithelium itself poses a structural barrier to inhaled challenges. At the apical pole of cell-cell interfaces, the tight junction, a large complex of proteins that functions as a fence, separates the apical and basolateral epithelial compartments and restricts flow through the paracellular space.Two transmembrane components of tight junctions are occludin and the claudins. Both are tetraspanning proteins that extend their extracellular loops across neighboring cells. Claudins comprise a large family of 24 known members that form homo-and heterotypic associations with one another. In addition, claudins have recently been characterized as forming anion-/cation-selective pores within the paracellular space; selectivity is regulated by the specific claudins that associate across the membrane (4,23,25). Thus the claudin expression profile, as well as how claudins interact with one another, largely regulates the epithelial selectivity for cation/anion transport. In addition, together with occludin, the tight junction forms a seal, demarcating the apical and basolateral membranes. Electron microscopic analysis of the tight junction shows that this protein complex forms a continuous, anastomosing array of fibrils that circumscribes each epithelial cel...

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